In Mutant Turtles chronology, Yoshihama Takeshi (よしはまたけし) was a ninja in Japan who was exiled from his homeland. Arriving in New York City and living in the sewer with rats and turtles, they eventually came in contact with a strange mutagenic substance which transformed Takeshi into a rat man and anthropomorphized the turtles. Takeshi taught the turtles ninjutsu and raised them as his sons, and the turtles nicknamed him Splinter.
After the turtles ended up saving reporter April O'Neil from a group of thugs, they brought her to their home and when she came to, Splinter told her of their origin.
Later, Splinter came across the mobile fortress of his arch-nemesis Sawaki Oroku, the Technodrome, and was captured. The turtles ventured in and rescued him.